Rinse the Test Cylinder with the sample water before proceeding. Fill the cylinder with 20ml of the sample water and add 5 drops of the CO2 TEST 1 Add 1 drop of the CO2 TEST 2 and gently shake the cylinder. The water will turn pink, and gradually get pale Continuously add 1 drop of CO2 TEST 2 at a time, gently shaking between drops, until the water stays pink for 60 seconds without changing. 1 drop of TEST 2 = 2mg/L 10 drops of TEST 2 = 20 mg/L The appropriate CO2 concentration in a plant aquarium should be 20-30mg/L